diff --git a/src/types.rs b/src/types.rs
index b6250f2..b62a13b 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -472,7 +472,8 @@ pub struct Form {
     pub(crate) max_field_size: usize,
     pub(crate) max_files: u32,
     pub(crate) max_file_size: usize,
-    pub(crate) transform_error: Option<Arc<dyn Fn(crate::error::Error) -> actix_web::Error>>,
+    pub(crate) transform_error:
+        Option<Arc<dyn Fn(crate::error::Error) -> actix_web::Error + Send + Sync>>,
     inner: Map,
 }
 
@@ -500,7 +501,7 @@ impl Form {
     /// Add an optional error handler to transform errors produced by the middleware
     pub fn transform_error(
         mut self,
-        f: impl Fn(crate::error::Error) -> actix_web::Error + 'static,
+        f: impl Fn(crate::error::Error) -> actix_web::Error + Send + Sync + 'static,
     ) -> Self {
         self.transform_error = Some(Arc::new(f));